The development of pharmaceuticals is now undergoing various searching investigations made in the attempt to exploit novel compounds having an excellent efficacy and at the same time to further increase the efficacy of these novel chemical substances or of such chemicals that have already been in use as pharmaceuticals by changing the dosage form or by optimizing the dosage regimen.
For example, with the purpose of prolongating the duration time of medicines which have a short half-life period which is regarded as the parameter for the effective duration time of medicines in the body, there have been considerable activities to develop sustained release pharmaceuticals which are made to have a concentration between the minimum effective concentration or higher and the maximum safety concentration or lower, so that the effective ingredients may be absorbed into the human body in the whole range of effective blood concentration extending over a long period of time.
As examples of sustained release pharmaceuticals, there are pharmaceutical preparations for percutaneous administration use such as ointments and aerosols. Since these preparations are applied to the skin at a rough estimate, their dosages differ from time to time and in the case of ointments, they sometimes cause trouble to the users by smearing their clothes. Furthermore, drugs contained in an ointment are taken into the body through the skin of a user by absorption while under such influences as concentration of the drugs contained in the ointment, thickness of the applied ointment, diffusion speed of the drugs in the substrate of an ointment, and absorption speed through the skin, thus building up so many factors as to cause uncertain conditions at the time of administration, and accordingly ointments have a problem of being not satisfactorily usable as pharmaceutical preparation whose effective concentration and adverse side effects are taken into serious consideration.
With the object of curing such defects, there are tape plasters and sticking plasters which are made to contain a certain amount of drugs in their adhesive layer and to have a certain handy size (Japanese Patent Laid-Open Publication 116011/'82 and 134020/'83).
By use of tape plasters and sticking plasters, many problems which occur with the use of ointments and aerosols can be solved.
However, since tape plasters and sticking plasters are used by making the drug-containing adhesive layer stick to the skin, they often cause an inflammation of the skin where they were adhered to. There is another problem: when the used tape plasters or sticking plasters are removed for renewal, the stratum corneum which forms the skin surface is damaged and if tape plasters or sticking plasters are repeatedly applied to the same site of application as before a change in the speed of absorbing the drugs takes place.
Also, since the skin has its effect on the metabolism including the release of water, it is avoided to make the adhesion area extremely large. It has, therefore, been regarded that drugs of low percutaneous absorption rate are not suited for percutaneous administration use.
There is still another problem: these tape plasters or sticking plasters, once get wet as in case of taking a bath, become apt to fall off, and the wet plasters hardly retain their adhesiveness to the skin and have to be discarded in spite of enough residual drugs left in them.